Synthetic oil containing a rare earth metal diester phosphate



United States Patent O 2,983,678 SYNTHETIC OIL CONTAINING A RARE EARTH METAL DIESTER PHOSPHATE John P. Pellegrini, Jr., and Harold 0. Strange, Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Dec. 31, 1958, Ser. No. 784,021

15 Claims. (Cl.'25232.5)

This invention relates to a new class of chemical compounds which are useful as addition agents to lubricating oils and oil compositions containing the same, and more particularly the invention relates to synthetic lubricating oil compositions containing a rare earth metal salt of a diester of o-phosphoric acid as a viscosity improving agent. By the term rare earth metal salts, we mean the salts of the elements of atomic numbers 57 to 71, inclusive. thanum, cerium, praseodym'ium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutecium. By the term synthetic lubricating oil, we mean a compound or composition of non-mineral origin having a majority of the lubricating properties of a mineral oil of lubricating grade.

The viscosity-temperature relationship of a lubricating oil is one of the more important characteristics of an oil in that it is this relationship which is indicative ofthe relative change inviscosity of an oil at high and low temperatures. As might be expected, the viscosity of most lubricating oils changes rapidly with a change in temperature. In general, oils tend to become thinner as their temperature increases and thicker as their temperature decreases. Thechange in viscosity with temperature is greater with some oils than with others. While some change is tolerable, excessive change is undesirable particularly when the oil is usedin lubricating mechanisms under elevated temperatures and pressures. In lubricating both automotive and aircraft engines, it is desirable for the lubricating oil to have a viscosity which is sufficient-ly high at an elevated temperature to provide adequate lubrication and to prevent excessive oil consumption; On the other hand, the lubricating oil should have a viscosity which is sufficiently low at atmospheric temperature to provide ease of engine starting. Increasing the high temperature viscosity of an oil while decreasingits low temperature viscositycan be accomplished only by improving the viscosity-temperature relationship, or stated differently, by raisingv the viscosity index of the oil.

Synthetic lubricating oils have been produced which have high viscosity indices. In the past, for example, certain aliphatic dibasic' acid esters have been prepared and have been found to possess high viscosity indices and many of the properties of mineral oils of lubricating grade but these esters have not been entirely satisfactory. Many of such esters, for example, while having high viscosity indices and many of the properties of a mineral oil'are. too thin for use as lubricants in some applications, particularly where the esters are used as gear lubricants in The rare earth elements thus include laner r 2,983,678

1 Vl'e'atented May- 9,

turbo-prop engines. Such lubricants require extremely high load-carrying characteristicsnot possessed by esters which have relatively low initial viscosities. While some viscosity increasing agents have beendevelop'ed which impart load-carrying characteristics to ester lubricants, the viscosity improving characteristics are lost or their effectiveness substantially reduced when the oil in which they are incorporated is subjected to vigorous agitation and high shear rates and stresses.

We have discovered that a composition having improved viscosity characteristics and lubricating properties over a wide temperature range can be prepared by incorporating a small amount of a rare earth metal salt of a diester of o-phosphoric acid in a synthetic lubricating oil. We have found, for example, that the addition of a small amount of a rare earth metal salt of a diester of o-phosphoric acid to a lubricant comprising an ester of an aliphatic dibasic acid increases the viscosity andviscosity index of the lubricant. We have found further that a lubricating composition comprising a major amount of an aliphatic. dibasic acid ester and a minor amount of a rare earth metal salt of a diester of o-pho'sphoricacidhas a surprising viscosity characteristic in that the vi's cosity of the lubricating composition increases to a maxi-'* mum as the temperature of the composition increases above about 100 F. The composition of the invention has a further surprising characteristic in that its viscosity index increases when subjected to vigorous agitation and high shear rates and stresses even though such treatment gives rise to a slight decrease in its viscosity.

The synthetic lubricating oil to which the rare earth metal salt of a diester of o-phos'phoric acid is added according to the invention is advantageously an aliphatic dibasic acid ester having a majority of the properties of a mineral oil of lubricating grade. If desired, a mixture of esters may be employed instead of a single ester. While the invention is primarily concerned with ester lubricants having initial viscosities which are too low foruse as a lubricant incertain applications such as in lubricating gears in turbo-prop engines, we do not wish to limit the invention in this regard inasmuch as the rare earth metal salts of the type disclosed more ,fully hereinbelow have the property of increasing the viscosity of lubricating oil, the ester lubricants should be substantially Free acids tend to catalyze the oxidation, of

neutral.

7 the esters, resulting in compounds which are corrosive to metals.

Therefore, to produce a lubricating composition which is stable and which is substantially non-corrosive to metals, we employ esters preferably having a neutralization number below about 0.2.

Exemplary of some of the esters to which the rare earth metal salts can be added accordingto the present assasva inventions are the diesters of'aliphatic dibasic acids and alcohols containing at least four aliphatic carbon atoms, preferably between 6 and Y16 carbon atoms.

Specific examples of some of the alcohols which can be used in preparing the aliphatic dibasic acid esters are l-butanol; Z-butanol; Z-methyl-Z-propanol; l-pentanol; Z-pentanol; 2-methyl-2-butanol; l-hexanol; Z-hexanol; 3- hexanol; 2 methyl l pentanol; 3- methyl l pentanol; 4-methyl-l-pentanol; 2,4-dimethyl-2-pentanol; 2,

B-dimethyl-S-pentanol; 2,4-dimethyl-3-pentanol; 3-ethyl- 3-pentanol; Z-methyl-l-hexanol; S-methyl-l-hexanol; 2-

anol; 5 methyl-3-hexanoli Lheptanol; Z-heptano'l; 4-'

alcohol; stearyl alcohol; glycol; glycerol; and the like, as

well as mixtures of two or more of such alcohols.

.The' so called 0x0 octyl alcohols, which, as is known, are highly branched chain saturated aliphatic monohydric alcohols prepared by the Oxo" process exemplify a class of commercially available alcohol mixaliphaticradical and one long chain aliphatic radical.

tures, which are suitablefor use in preparing synthetic lubricating oils for the purposes of the. invention. The

v0x0 process, briefly, involves the hydroformylation of olefinic hydrocarbons, followed by hydrogenationofthe carbonylic compounds thus obtained. Normally, the ole fim'c hydrocarbons used in the manufacture of oxo-octyl alcohols are prepared by condensation of C and C olefiins in the usual proportion in which they occur inpetroleum refinery gases. ,In thiscase, oxo-octylalcohols normally will; contain .arnixture of. branched-chained isomers of 'octyl. alcohol, and. the mixture will consist mostly. of isomeric dimethylhexanols. Although the above-indicated composition is the most common for" oxoocty-l alcohols, it will be appreciated that the proportions of the mixed isomeric alcohols can be varied to some extent by varying the proportions of the C and C olefins used in preparing the C olefin to be hydroformylated.

Specific examples of some of the dibasic acids with which the above-enumerated alcohols can be reacted in preparing the esters for use in the compositions of the present invention are oxalic, malonic, succinic, isosuccinic, glutaric, ethyl malonic, pyrotartaric, adipic, pimelic, suberic, azelaic, sebacic, and phthalic acid. When a low molecular weight acid is esterfied, a high molecular weight alcohol is preferred in order to produce an ester having a majority of the properties of a mineral oil of lubricating grade. While the diesters of the aliphatic dibasic acids are preferred, the esters of aromatic dibasic acids such as the phthalic acid ester of a material such as castor oil or other high molecular weight alcohols can also be used.

Specific examples of preferred synthetic lubricants to which the rare earth metal salt of a diester of o-phosphoric acid is added according to the invention are the substantially neutral esters of hexyl, octyl, decyl, lauryl, myristic and cetyl alcohols and adipic, pimelic, suberic, azelaic and sebacic acids. Specific examples of especially efiective ester lubricants are di-Z-ethylhexyl azelate, di-2-ethylhexyl sebacate, di-isooctyl azelate and di-isooctyl sebacate. t

The esters can be prepared by any of the methods known in the art. According to one method, as described in U.S. Patent No. 2,091,241 which issued on August 24, 1937, to H. M. Kvalnes, a discarboxylic acid or its anhydride is dissolved in an inert solvennafter which the t resulting mixture is heated to its boiling point.

While maintaining the mixtureat its boiling point, an alcohol to give the desired ester is added gradually. When addition of the alcohol is completed, the solvent'is distilled off and esterification is carried out at a temperature above 150 C. According to another suitable method, the alcohol and acid are reacted at an elevated temperature in the presence of a sulfuric acid catalyst. As the reaction proceeds, water is. continuously removed by azeotropic distillation with a solvent such as benzene or toluene. When the reaction is substantially complete, the product is washed with dilutealkali to removeany acidic. substances. Purification of the product may be accomplished by fractional distillation.

The particular synthetic lubricant employed, as well as the exact amount of such lubricant, depends upon the lubricant comprises an ester'of an aliphatic dibasic acid,

characteristics desiredin the final lubricating composition. In most instances, however, when the synthetic the esterof the aliphatic. dibasie acidcomprises at least 95 per cent by weight of the total composition.

The rare earth metal salts .of the o-phosphoric acid esters which can be usedin accordance with the, invention are those which are soluble in the synthetic oil and insoluble in water. In this regard, we prefer to employ a rare earth metal salt of a diester of o-phosphoric acid wherein'the ester substituents comprise one short chain,

The short chain radical'preferablycontains from 1 to 3 carbon atoms and the long chain radical preferably concontains from 14- to l6 carbon atoms for a saturated group and from 18 to 20 carbon atoms or more for an unsaturated group.

The rare earth metal salt of the diester of o-phosphoric acid can be prepared by anysuitable method. According to a preferred procedure, therare earth metal salt of the o-phosphoric acid ester is prepared by reacting a basic rare earth metal compound with an acidic o-phosphoric acid ester. The rare earth metal compound is employed in an amount sufficient to effect complete neutralization of the o-phosphoric acid ester. In some instances, the neutralization reaction takes place spontaneously, or substantially so, with the evoltion of heat. In other instances, however, it is required to add additional heat to effect complete neutralization. In effecting complete neutralization, it ispreferred to maintain the reaction temperaturebelow about 220 F. in order to avoid appreciable decomposition of the resulting salt. After salt formation is substantially complete, the mixture is further heated for a time sulficient to expel the water of neu- ;tralization. The use of a slight vacuum at this point faciltates dehydration. I'hereafter, the dehydrated product is filtered to separate out any unreacted rare earth metal compound. In some instances, it is desirable to prepare an alkali metal salt of the organic phosphate and thereafter prepare the rare earth metal salt by metathesis of the alkali metal salt with a water-soluble salt of the rare earth metal such as the nitrate; chloride or sulfate, as

appropriate. a p

The rare earth metal compound used in preparing the corresponding metal salt of the diester of o-phosphoric acid can be either a relatively pure compound or it can he. a mixture .of the rare earth compounds such as are found in monazite and bastnasite. The following table shows the composition of rare earths in typical commercial rare earth salts.

TABLE I Composition of Rare Earths, Wt. Percent as Oxides While the individual rare earth metal oxides can successfully be employed in preparing the salt of the diester of o-phosphoric acid, compounds of the individual elements are more expensive because of the'increasing difliculty of separating the individual elements. Therefore, from an economic standpoint it is desirable to prepare the rare earth metal salt of a diester of o-phosphoric acid by. neutralizing the o-phosphoric acid ester with a mixture of the rare earth oxides.

The acidic o-phosphoric esters used in making the rare earth metal salts for the purposes of the invention also may be prepared in any suitable manner. For example, a mixture of a higher monohydric alcohol containing from 8 to 20 carbon atoms, a monohydric alcohol containing from 1 to 3 carbon atoms and phosphorus pentoxide may be refluxed for several hours. The complex mixture of mono, di and tri esters may be distilled to obtain individual pure compounds.

According to another embodiment, phosphorus oxychloride is reacted with a monohydric alcohol containing from 1 to 3 carbon atoms to form the corresponding phosphoryl dichloride which is thereafter reacted with a monohydric alcohol containing from 8 to 20 carbon atoms to form a posphoryl monochloride which is subse-' quently hydrolyzed to form the desired phosphoric acid diester containing a C to C aliphatic radical and a C to C aliphatic radical. Examples of the short chain alcohols are methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol and allyl alcohol. Examples of the long chain alcohols are n-octyl, isooctyl, nonyl, decyl, n-dodecyl (lauryl), tetradecyl, n-hexadecyl, n-octadecyl (stearyl), n-octadecenyl (oleyl), n-octadecadienyl (linoleyl) and eicosyl alcohols. The alcohols need not be pure as mixtures of two or more can be used.

Organic phosphates that form suitable rare earth metal Salts for the purposes of this invention are diesters of "o-phosphoric acids whose two ester substituents are aliphatic radicals one of which contains from 1 to 3 carbon atoms and the other contains from 8 to 20 carbon atoms.

, Examples of such organic diesters of phosphoric acids are methyl n-octyl, ethyl n-octyl, n-propyl -n-octyl, isopropyl isooctyl, allyl isooctyl, methyl nonyl, ethyl nonyl, propyl nonyl, methyl decyl, ethyl decyl, propyl decyl, methyl dodecyl, ethyl n-dodecyl (ethyl lauryl), allyl n-dodecyl, ethyl tetradecyl, ethyl n-hexadecyl, ethyl n-octadecyl (ethyl stearyl), allyl n-octadecyl, ethyl n-octadecenyl (ethyl oleyl), ethyl n-octadecadienyl (ethyl linoleyl), and ethyl eicosyl esters of o-phosphoric acid.

Specific examples of especially effective agents for the purposes of the invention are the oil-soluble lanthanum and neodymium salts of ethyl oleyl acid orthophosphates. Othersalts included by the invention are the lanthanum, neodymium, praseodymium, cerium and samarium salts of ethyl n-octyl, ethyl isooctyl, ethyl decyl, ethyl n-dodecyl (lauryl), ethyl n-octadecyl (stearyl) and ethyl n-octadecenyl acid orthophosphates.

The preparation of the salts for use in the compositions I of the invention are illustrated by the following specific'ex- 'amples.

EXAMPLE I Lanthanum ethyl oleyl orthophosphate Into a 3 liter round bottom flask equipped with a mechanical stirrer, condenser and dropping funnel are placed 89.2 gm. of ethyl oleyl acid orthophosphate, 400 ml. of

' aesae'is water and 250 ml. of 95% ethanol. To the mixture thus formed are added, with stirring, 9.49 gm. sodium hydroxide in 200 ml. of water. The temperature of the reaction is maintained at about 25 C. To the reaction mass thus formed are slowly aded 34.2 gm. of lanthanum nitrate hexahydrate in 200 ml. of water with rapid stirring, the temperature of the metathesis reaction being maintained at about 25 C. A gummy yellow precipitate is formed. The water isdecanted from the reaction mass and thereafter the precipitate is dissolved in hexane, solution being facilitated by the application of a small amount of heat. Thereafter, the product is. filtered to remove any undissolved solids. Solvent is then stripped from the filtrate. When the solvent is completely removed, an opaque yellowish rubber-like product comprising lanthanum ethyl oleyl phosphate is obtained.

Analysis of the product shows it to compare favorably with the theoretical analysis of lanthanum ethyl oleyl orthophosphate as follows:

The rare earth metal salts of the ophosphoric acid esters can be employed per se or they can be added to the lubricating oil in the form of an oil concentrate. In preparing the oil concentrate, the rare earth metal salt can be prepared in an organic solvent which can be flashed from the oil after formation of the concentrate. Organic solvents suitable for this purpose include hexane, isooctane, naphtha, benzene, toluene, carbon tetrachloride, and the like. When an oil concentrate is prepared first, the concentrate can be added directly to the oil to be improved or it can be admixed with one or more other improving agents. Regardless of whether the rare earth metal salt of the o-phos'phoric acid ester is employed per se or in the form of an oil concentrate, an amount is used suificient to impart improved viscosity characteristics to the oil. The rare earthmetal salts are useful when employed in amounts of about 0.1 to about 5 percent by weight based on the weight of the total oil composition. Excellent viscosity index improvement has been obtained by the use in an ester of an aliphatic dibasic acid such as, di-isooctyl azelate, of amounts of the lanthanum salt of ethyl oleyl o-phosphate between 0.1 and 0.6 percent by weight of the composition. When the rare earth metal salt is employed in an amount inexcess of about 0.6 percent, the composition is more viscous at 210 F. than it is at F. When lanthanum ethyl oleyl o-phosphate is employed in amounts between about 0.5 and 1 per cent, the viscosityof the composition increases as the temperature of the composition increases from about 10 to about F. When the amount of the lanthanum salt is increased to about 2.5 percent, the viscosity of the composition increases'to a maximum as the temperature increases to about F. When the amount of the lanthanum salt is increased still further to about 5 percent by weight of the total composition, the viscosity of the composition continues to increase with the temperature as the temperature is raised from about 100 to about 200 F With a cerium salt of ethyl oleyl o-phosphate, the viscosity continues to increase even at a temperature above 200 F. It will be understood therefore, that the optimum amount of the rare earth metal salt will vary depending upon the characteristics desired in the final composition. A slight variation in the optimum amount of salt required for a given result will also vary with the synthetic lubricating oil base and with the particular rare earth salt employed.

The following examples illustrate the preparation of oil concentrates of the various rare earth metal salts of o-phosphoric acid esters. The oil used in the examples is a synthetic oil (di-isooctyl azelate having as typical characteristics a viscosity of 12.7 and 3.4 centistokes at EXAMPLE LII Neodymium ethyl oleyl orthophosphate Into a 2 liter round bottom flask equipped with a mechanical stirrer and reflux condenser are placed 970 gm. of di-isooctyl azelate. To the mass of synthetic oil are added 4.0 gm. of neodymium oxide and 26.65 gm. of ethyl oleyl o-phosphoric acid with rapid stirring. The addition of several cubic centiemeters of water at this point is advantageous in order to increase the speed of the reaction. The reaction mass thus formed is heated at 75 C. for several hours with continued stirring. Heating is continued for from 1 to 3 or 4 hours or until the reaction is substantially complete. When the reaction is complete, the water is removed from the reaction product under a reduced presure at about 75 to 80 C. The heated solution is then filtered to remove any unreacted neodymium oxide. The filtered oil thus obtained is light in color and is fairly viscous, comprising a 3% solution of neodymium ethyl oleyl orthophosphate in di-isooctyl azelate.

EXAMPLE III Lanthanum ethyl oleyl orthophosphate Into a 3 liter round bottom flask are placed 970 gm. of di-isooctyl azelate, 26.7 gm. of ethyl oleyl o-phosphoric acid and 4.0 gm. of lanthanum oxide. To this mixture are added 5 ml. of water followed by heating at 80 C. with stirring for 3 hours. The water is then removed by heating under a vacuum at 80 C. The heated product is then filtered to remove excess lanthanum oxide. the viscous synthetic oil solution cools it becomes somewhat less viscous, and sufficieutly fluid to flow. The product comprises a 3% solution of lanthanum ethyl oleyl orthophosphate in di-isooctyl azelate.

EXAMPLE IV Lanthanum ethyl lauryl orthophosphate In a 2 liter round bottom flask are placed 760 gm. of di-isooctyl azelate, 34.6 gm. of ethyl lauryl phosphate and gm. of lanthanum oxide. To this mixture are added 10 m1. of water followed by heating for 4 hours at 95 C. Upon completion of the reaction, the water is removed by heating under a vacuum at about 95 C. The heated product is then filtered to remove excess lanthanum oxide. The viscous filtered oil product which becomes somewhat less viscous when it cools comprises a 5% solution of lanthanum ethyl lauryl orthophosphate in di-isooctyl azelate.

EXAMPLE V Cerium ethyl oleyl orthophosphate Into a 2 liter flask are placed 1170 gm. of di-isooctyl azelate, 26.7 gm. of ethyl oleyl orthophosphate, ml. of water and cerium hydroxide obtained by reacting 17 gm. of cerium nitrate with ammonium hydroxide. The reaction mass is heated to 75 to 80 C. and dehydrated as in the previous examples. The product comprises a 2.5% solution of cerium ethyl oleyl orthophosphate in iii-isooctyl azelate.

. EXAMPLE VI Praseodymium methyl oleyl orthophosphate Praseodymium oxide and methyl oleyl orthophosphate are admixed with a small amount of water and added to di-isooctyl azelate as in Example IV. Upon heating and removal of the water as in Example IV, a solution When of praseodymium methyl oleyl orthophosphate in di-isooctyl azelate is obtained.

EXAMPLEVII I 'Sama'rium ethyl oleyl orthophosphate The procedure of Example III is followed except samarium oxide is substituted for lanthanum oxide. The product comprises a solution of samarium ethyl oleyl orthophosphate in di-isooctyl azelate.

EXAMPLEY I Lanthanum ethyl isooctyl orthophosphate j I Neodymium methyl eicosyl orthophosphate o The procedure of Example II is followed except methyl eicosyl o-phosphoric acid is substituted for the ethyl oleyl o-phosphoric acid. The resulting product comprises a solution of neodymium methyleicosyl orthophosphate in di-isooctyl azelate.

EXAMPLE x Lanthanum propyl oleyl orthophosphate The procedure of Example IV is followed except propyl oleyl orthophosphate is substituted for ethyllauryl phosphate. The resulting product comprises a solution of lanthanum propyl oleyl orthophosphate in di-isooctyl azelate. t

It will be understoodthat the foregoing examples are illustrative only and that other rare earth metal salts of diester orthophosphates wherein the ester substituents comprise one short chain aliphatic radical containing from 1 to 3 carbon atoms and one long chain aliphatic radical containing from 8 to 20 carbon atoms can be employed. Specific examples of such other salts include the europium, gadolinium, terbium, dysprosium, holium, erbium, thulium, ytterbium and lutecium salts of methyl oleyl, ethyl oleyl, .propyl oleyl, ethyl isooctyl, ethyl eicosyl and allyl lauryl orthophosphoric acid. 3 While the preparation of the rare earth metal salts according. to the procedure given in Examples 11 to X utilizes di-isooctyl azclate as the solvent, it will' be understood that the rare earth metal salts useful for the purposes of the invention can be obtained in the free state, as in Example I, just as readily as they are obtained in oil blends. To obtain the free rare earth metal salt of a diester orthophosphate, a more volatile solvent, such as hexane, benzene and carbon tetrachloride, is used in place of a synthetic oil and is flashed oil either before orafter the formation of the rare earth salt. When the salt is obtained in the form of an oil concentrate, the oil solvent is preferably the same as the base oil to which the salt is to be added. The use of a different oil solvent may result in an oil concentrate which is difiicultly soluble or insoluble inthe oil to be improved.

To demonstrate the effectiveness of the rare earth metal salts of the type described above in a synthetic oil composition contemplated by thisinvention, we have conducted several comparative, tests, the results'of which are listed below, with a representative synthetic oil alone and withthe same'oil blended with various representative rare earth metal salts of diester orthophosphatesl These tests were conducted with an ester of an aliphatic dibasic acid, di-isooctyl azelate. The efliect on the viscosity and viscosity index characteristics of di-isooctyl azelate by the addition thereto of various representative rare earth metal salts of diester o-phosphates is clearly shown by the illustrative data in Table II.

TABLE II Oompyositton, percent y Weight Didsooctylazelate Lanthanum ethyl oleyl .or-fhosphatp Ce um ethyl oleyl o-Phosph Lanthanum ethyl lauryl o-Phosphate.

VISCOSITY nun Viscosity, cs.: at 100 F Viscosity Index Viscosity: centipoise at 100 Viscosity: centipoise at 102 Viscosity: centipoise at 215 F. 4 Viscosity: centipoise at 217 F The data in the above Table 11 clearly show that the addition of as little as 0.25 percent of the lanthanum salt of ethyl oleyl'o-phosphate greatly improves the viscosity index of di-isoctyl azelate. It will be noted further that when amounts of lanthanum ethyl oleyl o-phosphate in excess of about 0.6 percent were employed (Compositions F, G and H), the compositions were more viscous at 210 F. than they were at 100 F. The thickening effect obtained by increasing temperatures is also illustrated in Compositions I and I wherein cerium ethyl oleyl o-phosphate and lanthanum ethyl lauryl o-phosphate in amounts of 2.5 and 5.0 percent respectively were added to di-isooctyl azelate. This result is indeed surprising.

The surprising effect of heat on an oil composition of the invention containing at least about 0.6 percent of lanthanum ethyl oleyl phosphate is shown by the data in Table III. The effect of heat is also shown in connection with compositions of this invention containing the neodymium and cerium salts of ethyl oleyl o-phosphate and lanthanum ethyl lauryl o-phosphate.

TABLE III the lubricant is more viscous at 210 F. than it is at F. The efiect of temperature on a lubricating composition of the invention is thus contrary to the effect of temperature on the synthetic base oil alone as well as the effect on oils in general. It will be noted further that when the di-isooctyl azelate contains between about 0.5 and 1 percent of the lanthanum salt of ethyl oleyl o-phosphate, the viscosity increases with temperature to a maxi! mum at about F. When the lanthanum ethyl oleyl o-phosphate is increased to about 2.5 percent, the viscosity continues to increase at temperatures up to about F. When the lanthanum salt is further increased to 5 percent, the viscosity continues to increase at a temperature up to about 200 F. With the cerium salt, the viscosity still continues to increase at a temperature in excess of 215 F.

The ability of the oil compositions of the invention to retain improved viscosity characteristics even though subjected to prolonged ultrasonic irradiation is demonstrated Composition, percent by Weight Di-isooctyl azelate- 100 Lanthanum ethyl oleyl o-phosph ate Neodymium ethyl oleyl o-phosphatem- Cerium ethyl oleyl o-phosphate Lanthanum ethyl lauryl o-phosphate- VISCOSITY DATA Viscosity, centipoise:

at 100 F ozemoeus I l Centisto :es. FQentistokes at 210? F.

The data in the 'above Table III clearly show that when the rare earth metal salts of ethyl oleyl o-phosphate and ethyl lauryl o-phosphate are employed in amounts in exby the data shown in Table IV. These comparative tests were made with di-isooctyl azelate alone and with the same synthetic oil blended with a representative rare earth cess of 0.6 percent, a surprising result is obtained in that 75 metal salt of a diester orthophosphate.

TABLE IV Composition: Percent By weight U V Di-isooctyl azelate 100 99. 4 Lanthanum ethyl oleyl mphosphate. 0. 6

Viscosity Data:

Irradiation time (min- Viscosity, cs. utes): and VI at- 100 12. 66 15.83 210 3. 40 16. 72 VI 165 100 12. 67 14.99 30 210 3. 43 12. VI 168 195 100 12.71 13. 93 60 210 3. 41 9. 7 VI 165 20 100 12.75 14. 0 90 210 3. 42 9, 7 VI 165 20 100 12.84 13. 51 120 210 3. 44 5. 90 VI 166 225 Theimprovement obtained in viscosity index by the improving agents of the present invention is clearly shown by the illustrative data in Table IV. It will be noted thatwhile ultrasonic irradiation caused some decrease in the viscosity of the composition of the invention, i.e., Composition V, both at 100 F. andat 210 F., the ir radiated composition in every instance had viscosities above the viscosity of the synthetic oil alone. It will be noted further that the composition of the invention has a surprising charactaristic in that its viscosity index in creases with prolonged ultrasonic irradiation.

An inspection of the physical properties of di-isooctyle azelate and the same ester lubricant containing 0.6 percent by weight of lanthanum ethyl oleyl o-phosphate are as follows:

The synthetic oil composition of this invention can contain other addition agents normally added to oils for a specific purpose such as an oiliness and extreme pressure agent, an anti-oxidant, a corrosion inhibitor, a foamsuppressant, a dye, a sludge inhibitor, and the like. p

The compositions of our invention comprise useful damping fluids in electronic controls, gear lubricants for automotive and aircraft engines, insulating oils, greaseforming fluids, and the like.

While our invention has been described with reference to various specific examples and embodiments it will be understood that the invention is notlimited to such examples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A composition consisting essentially of a major amount of a substantially neutral ester of a dibasic acid containing 2 to IOcarbon atoms and an aliphatic alcohol containing 2 to 18 carbon atoms and a minor amount, sufficient to impart improved viscosity characteristics to said ester, of a rare earthmetal salt of a 'diester of o-' phosphoric acid wherein the'rare earth metal is an ele ment having an atomic number from 57 to 71 and the ester substituents comprise one aliphatic radical containamount is about 0.1 to about 5 percent by weight of the composition. i

3. A composition consisting essentially of, a major amount of a substantially neutral ester of a dibasic acid M containing 2m 10 carbon atoms and an aliphatic alcohol containing 4 to 18 carbon atoms and a minor amount, ,sufiicient toimpart improved viscosity characteristics to said ester, of a rare earth metal salt of a diester of ophosphoric acid wherein the rare earth metal is an e1emerit having an atomic number from 57 to 71 and the ester substituents compriseone aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radical containing from 8 to 20 carbon atoms.

- 4. A composition consisting essentially of a major amount of a substantially neutral ester of a dibasic acid containing 2 to 10 carbon atoms and an aliphatic alcohol containing 6 to 16 carbon atoms and a minor amount, sufficient to impart improved viscosity characteristics to said ester, of a rare earth metal salt of a diester of o-phosphoric acid wherein the rare earth metal is an element having an atomic number from 57 to 71 and the ester substituents comprise one aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radical containing from 8 to 20 carbon atoms.

5. A composition consisting essentially of a major amount of a substantially neutral ester of an aliphatic di basic acid containing 6 to 10 carbon atoms and an aliphatic alcohol containing 6 to 16 carbon atoms and a minor amount, sufiicient to impart improved viscosity characteristics to said ester, of a rare earth metal salt of a diester of o-phosphoric acid wherein the rare earth metal is an element having an atomic number from 57 to 71 and the ester substituents comprise one aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radical containing from 8 to 20 carbon atoms.

6. A composition consisting essentially of a major amount of a substantially neutral ester of an aliphatic dibasic acid containing 6 to 10 carbon atoms and an aliphatic alcohol containing 6 to 16 carbon atoms and a minor amount, sufficient to impart improvedviscosity characteristics to said ester, of a lanthanum salt of a diester of o-phosphoric acid wherein the ester substituents comprise one aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radical containing from 8 to 20 carbon atoms.

7. A composition consisting essentially of a major .amount of a substantially neutral ester of an aliphatic dibasic acid containing 6 to 10 carbon atoms and an aliphatic alcohol containing 6 to 16 carbon atoms and a minor amount, sufficient-to impart improved viscosity characteristics to said ester, of a cerium salt of a diester of ophosphoric acid wherein the ester substituents comprise one aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radical containing from 8 to 20 carbon atomsa 8. A composition consisting essentially of a major amount of a substantially neutral ester of an aliphatic dibasic acid containing 6 to 10 carbon atoms and an aliphatic alcohol containing 6 to 16- carbon atoms and a minor amount, sufficient to impart improved viscosity characteristics to said ester, of a neodymium salt of a diester of o-phosphoric acid wherein the ester substituents comprise one aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radicalicontaining from 8 to 20 carbon atoms. 3 3

9. A composition consisting essentially of a major amount of a substantially neutral ester of an aliphatic dibasic acid containing 9 to 10 carbon atoms and an aliphatic alcohol containing 8 carbon atoms and a minor amount, suflicient to impart improved viscosity characteristics to said ester, of a rare earth metal salt of a diester of o-phosphoric acid wherein the rare earth metal is an element having an atomic number from 57 to 71 and the ester substituenlts comprise one aliphatic radical containing from 1 to 3 carbon atoms and one aliphatic radical containing from 8 to 20 carbon atoms.

10. A composition consisting essentially of a major amount of a substantially neutral ester of an aliphatic dibasie acid containing 9 to 10 carbon atoms and an aliphatic alcohol containing 8 carbon atoms and a minor amount, suflicient to impart improved viscosity characteristics to said ester, of a rare earth metal salt of ethyl oleyl orthophosphate wherein the rare earth metal is an element having an atomic number from 57 to 71.

11. A composition consisting essentially of a major amount of di-isoootyl azelate and a minor amount, suflicient to impart improved viscosity characteristics to said di-isooctyl azelate, of lanthanum ethyl oleyl orthophosphate.

12. A composition consisting essentially of a major amount of di-isooctyl azelate and a minor amount, sufiicient to impart improved viscosity characteristics to said di-isooctyl azelate, of neodymium ethyl oleyl orthophosphate.

13. A composition consisting essentially of a major References Cited in the file of this patent UNITED STATES PATENTS 2,285,853 Downing et al June 9, 1942 2,480,673 Reifi" et a1. Aug. 30, 1949 2,820,766 Elliott et al. a Jan. 21, 1958 OTHER REFERENCES Chem. Abstracts, vol. 52, 64g, Nov. 10, 1958. 

1. A COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF A SUBSTANTIALLY NEUTRAL ESTER OF A DIBASIC ACID CONTAINING 2 TO 10 CARBON ATOMS AND AN ALIPHATIC ALCOHOL CONTAINING 2 TO 18 CARBON ATOMS AND A MINOR AMOUNT, SUFFICIENT TO IMPART IMPROVED VISCOSITY CHARACTERISTICS TO SAID ESTER, OF A RARE EARTH METAL SALT OF A DIESTER OF OPHOSPHORIC ACID WHEREIN THE RARE EARTH METAL IS AN ELEMENT HAVING AN ATOMIC NUMBER FROM 57 TO 71 AND THE ESTER SUBSTITUENTS COMPRISE ONE ALIPHATIC RADICAL CONTAINING FROM 1 TO 3 CARBON ATOMS AND ONE ALIPHATIC RADICAL CONTAINING FROM 8 TO 20 CARBON ATOMS. 